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ICCT update finds real-world vehicle fuel economy gap continues to widen in Europe to 40%

The gap between official fuel-economy figures and the real world for new cars in the EU has reached 40 per cent, according to the latest update by the International Council on Clean Transportation (ICCT) to its on-going research into in-use vehicle fuel efficiency and CO2 emissions. (Earlier post.)

Since 2001, the discrepancy between official measurements of vehicle efficiency and actual performance of new cars in everyday driving has more than quadrupled—a discrepancy that now translates into €450 (US$500) per year in extra fuel costs for the average vehicle. The updated study closely follows on revelations that a similar gap in NOx emissions from diesel passenger vehicles was, at least in the case of Volkswagen, deliberately engineered, and as the European Commission prepares to adopt an improved test procedure that would produce more realistic vehicle test results.

The new study, jointly prepared by the ICCT, the Netherlands’ Organisation for Applied Scientific Research (TNO), and Germany’s Institut für Energie- und Umweltforschung Heidelberg (IFEU), describes the increasing real-world efficiency gap using systematic statistical analysis.

A technical definition of real-world driving is elusive because of variations in vehicle types, driving behavior, and driving conditions. Nonetheless, in aggregating data on almost 600,000 vehicles from eleven data sources and six countries, this study reveals a clear trend over time: the divergence (or “gap”) between real-world and official CO2 emissions increased from approximately 8 percent in 2001 to 40 percent in 2014. Each data source used for the study includes a unique set of vehicles and drivers, so estimates of the divergence of real-world from official values vary among them. however, the increase in the gap cannot be explained based on driving behavior or differences between the data sources, but is instead a result of increasingly unrealistic type-approval values.

—“From laboratory to road: A 2015 update”

Divergence between real-world and manufacturers’ type-approval CO2 emissions for various real-world data sources, including average estimates for private cars, company cars, and all data sources. Source: ICCT. Click to enlarge.

The analysis draws on data from a number of different sources: the user websites (Germany) and (United Kingdom); the leasing companies Travelcard (Netherlands) and LeasePlan (Germany); the car and consumer magazines Auto Bild (Germany), auto motor sport (Germany and Sweden), WhatCar? (United Kingdom), (Spain) and the car club TCS (Switzerland).

The researchers assessed in detail the underlying reasons for the growing divergence, and identified four key factors:

  • Chassis dynamometer testing. Under the EU regulation, there are a number of “loopholes” that can potentially be exploited by vehicle manufacturers during chassis dynamometer testing. These include break-in periods for the test vehicle, tolerances regarding laboratory instruments, the state of charge of the vehicle’s battery, special test driving techniques, and use of pre-series parts that are not representative of production vehicles. The ICCT analysis indicates that vehicle manufacturers have found ways to optimize chassis dynamometer type-approval testing over time, which at the same time made it less representative of average real-world driving conditions. As a result, the impact of chassis dynamometer testing flexibilities on the divergence between type-approval and real-world CO2 emissions today is estimated to explain more than half of the overall divergence observed.

  • Road load determination. Coefficients for road load are used to characterize the forces (mainly aerodynamic drag and rolling resistance) that a car needs to overcome as it is driven on the road. These coefficients are determined through a series of coast-down tests on an outside track. There are a number of aspects of this road load determination procedure that offer vehicle manufacturers potential for exploiting tolerances and flexibilities, ICCT said. These include tire selection and preparation, selection of the test track, ambient test conditions, and pre-conditioning of the vehicle, among others. The ICCT team estimated that about one-quarter of the overall gap observed in 2014 is explained by exploitation of tolerances and flexibilities in the methods required by the EU regulation for determining road load.

  • Technology deployment. Certain technologies, such as stop-start systems and hybrid powertrains, have a different effect on CO2 emissions in the type-approval procedure than they do during real-world driving, because of specific characteristics of the driving cycle used in type-approval testing that differ from typical everyday vehicle operation. ICCT estimated that about one-tenth of the gap in 2014 is explained by an increasing market share of those technologies.

  • Other parameters. Running air conditioning systems and entertainment systems increases fuel consumption during real-world driving. Nonetheless, these devices are either switched off or are not fully taken into account during the type-approval emissions test, leading to unrealistically low CO2 emission values. ICCT put the contribution of these factors at about another one-tenth of the gap in 2014.

For car manufacturers, the divergence puts those that want to report realistic CO2 emission values at a competitive disadvantage. unrealistic type-approval values also have the potential to damage manufacturers’ credibility and may erode consumer and regulator trust in the entire industry.

—“From Laboratory to Road: A 2015 update”

Manufacturers measure vehicle fuel consumption in a controlled laboratory environment, using a test procedure called the New European Driving Cycle (NEDC). This procedure was developed in the 1980s and was not originally intended to be used for fuel consumption testing. A new and more appropriate test procedure, the Worldwide Harmonized Light Vehicles Test Procedure (WLTP), has been developed through the United Nations and is ready for implementation in the EU as early as 2017.

Without introduction of the new test procedure, the WLTP, we expect that the gap will grow to about 50 per cent by 2020. The WLTP would cut the gap approximately in half, and should therefore be introduced in the EU by 2017.

—Dr. Peter Mock, Managing Director of ICCT Europe

The ICCT researchers warn that the WLTP will not resolve all open issues, and could itself inadvertently contain new loopholes that could lead to the performance gap to increase again in the future. Further actions are therefore required, in particular compliance testing of randomly selected production vehicles, they suggested.


  • Uwe Tietge, Nikiforos Zacharof, Peter Mock, Vicente Franco, John German, Anup Bandivadekar (ICCT), Norbert Ligterink (TNO), Udo Lambrecht (IFEU) (2015) From laboratory to road: A 2015 update


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This is more evidence about the grotesquely high influence that the European auto industry has on the European legislation that matters to them. They basically rig the legislation to suit their own interest and not the car buyers or the public. When real world MPG deviates by 40% to 50% from the tested MPG and the latter is used to market the cars it is fraudulent marketing which is illegal. Car buyers are deceived. We need to sue the automakers for misleading consumers and they need to pay up. If they do not pay they will continue to use these hypothetical MPG numbers for the marketing of their cars. The auto industry should be forced only to use real world MPGs in their marketing and pay billions of EUR if they cheat in this area.


I would love to have the UN come together and make a formal testing standard for both emissions and mpg calculations. Have it a standard for most of the world.

I personally don't care exactly how its done, but id like to get behind a car with a 10mpg rating and achieve =X and another car rated 20mgp and get close to 2x. As long as its consistent I dont care what the actual is.

I always chuckle at people saying mpg sucks, when they do 80+ on the freeway.


If the fleet as sold achieves the rated fuel consumption when driven according to the test cycle parameters, the issue comes down to how the fleet is used:

  1. How the drive cycle in use differs from the test cycle
  2. How the conditions in use differ from the test conditions

You can't expect a vehicle running with max A/C on a hot day in heavy traffic to work as it does on the test.  Neither can you expect a vehicle started after an extended cold-soak to have the same fuel economy as one operating in mild weather.

The real question is why the economy ratings are diverging from real-world figures over time.  It would not surprise me if drivers are reacting to better vehicle performance by driving them harder.  The answer to that is to change behavior.


EP, thanks for your comments... I don't always agree with you but you always give well thought out reasons/arguments. (I concur with this post though)

I agree with your performance assumptions... I mean minivans are faster than sports cars of the early 90s. Suddenly 140hp+ is needed for a subcompact/Bclass car.

I was thinking of making the test like the tread wear on the tires lol, I personally don't understand the numbers... but the higher the number the more life I am likely to get out of them.

MPGe also just should have never happened. Its should be watts per mile or Kw per mile... what ever would be easiest to standardize LD and heavy duty. EX: 0.400Kw/mile. I just find myself converting it to that anyway. What happens in 75years when gasoline is no longer refined? Its an electric car, there are no gallons except for washer fluid.

When I look at cars to purchase... I look at engine features, transmission type and drive ratios, tire size/cost, I read the owners manual looking at the maint. schedule, I look on forums looking for: common issues, fuel economy, modifications, general complaints. I don't really go in with any chance for surprises. I rarely look at the sticker, but the sticker is what it is, its a tool to help, not the end all be all of fuel economy.

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